Microflora Activities 

 and Decomposition 



P. W. Flanagan and F. L. Bunnell 



INTRODUCTION 



Decomposition results in the disintegration and mineralization of 

 organic residues. Most physical and chemical changes that occur in and 

 around the decomposing substrate cannot be separated from the effects 

 of microbial activity. However, degradation of plant and animal remains 

 may be well advanced before significant ingress of microbes occurs 

 (Dowding 1974, Flanagan and Veum 1974). Losses of weight and specific 

 chemical constituents, which are often considered as measures of decom- 

 position, may be initiated by plant-soil environment interactions that in- 

 duce senescence and autolysis in moribund tissue. Important ecological 

 phenomena that cause loss of weight from organic residues but occur 

 somewhat independently of microbial activity include leaching, micro- 

 faunal activities, and chemical reactions that influence mineralization. 



Soil invertebrates and protozoans are considered to influence de- 

 composition rates indirectly by modifying the activities of the decom- 

 poser organisms or microbes. They modify the environment through 

 comminution of organic matter, and the microbial populations by graz- 

 ing upon them (Chapter 11). Plant components Hke soil algae and the 

 roots of vascular plants alter the environment through the provision of 

 particular substrates and physical structure, and by modification of pH 

 and supply rates for oxygen and other chemical compounds. 



Decomposition of organic matter is accompanied by synthesis of mi- 

 crobial tissues which themselves decompose, contributing to further mi- 

 crobial production. If the amount of substrate is limited, the potential 

 for production of microbial biomass is dependent upon the efficiency of 

 the microbial population in solubilizing, assimilating and incorporating 

 organic remains, i.e. the efficiency of conversion of grams substrate to 

 grams microbe, or the yield coefficient. The yield coefficient is influ- 

 enced by climatic and substrate variables and is decreased significantly 

 by the maintenance demands of preformed and forming tissues (Gray 



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